Conventional Herbicide Research Articles

Comparative environmental impacts of glyphosate and conventional herbicides when used with glyphosate-tolerant and non-tolerant crops

The introduction of glyphosate-tolerant (GT) crops is expected to mitigate the environmental contamination by herbicides because glyphosate is less persistent and toxic than the herbicides used on non-GT crops. Here, we compared the environmental balances of herbicide applications for both crop types in three French field trials. The dynamic of herbicides and their metabolites in soil, groundwater and air was simulated with PRZM model and compared to field measurements. The associated impacts were aggregated with toxicity potentials calculated with the fate and exposure model USES for several environmental endpoints. The impacts of GT systems were lower than those of non-GT systems, but the accumulation in soils of one glyphosate metabolite (aminomethylphosphonic acid) questions the sustainability of GT systems. The magnitude of the impacts depends on the rates and frequency of glyphosate application being highest for GT maize monoculture and lowest for combination of GT oilseed rape and non-GT sugarbeet crops.

Is there a Weed Shift in Roundup Ready Maize?

AbstractThe cultivation of transgenic glyphosate-resistant crop varieties can simplify weed control in crops such as maize and others. On the other hand, the repeated use of broadly effective herbicides like glyphosate, especially in the same crop, can have a negative effect on biodiversity. Additionally there is a risk for a spread of more tolerant or even resistant weed species.It was the aim of a 6-years field study (2003-2008) to investigate weed effects of use of glyphosate in a continuous transgenic herbicide-resistant maize rotation at three sites in Germany. These sites differed significantly in terms of soil, climate and initial weed spectrum. The studies focussed on the comparison between local herbicide standards and split applications of Roundup Ready (360 g L^-1^ glyphosate) applied at dosages of 1,5 + 1,5; 2 + 2 and 3 + 3 L ha^-1^ Roundup Ready.Concerning the potential changes in weed communities over longer periods of time, the study did not indicate any negative effect on weed infestation, communities or diversity, of the glyphosate treatments compared to the local herbicide standard. Concerning species richness, there was no clear trend of the Roundup Ready treatments. Possible changes of the abundances of individual species were affected by the initial weed spectrum and consequently by the site conditions. As far as the conventional herbicides are efficiently used, they have no other effect than the glyphosate applications. Similar results were seen for the Shannon’s diversity index and Shannon’s evenness index.In sum, and looking at annual effects, it could be concluded from this 6 years study that 1) there are no statistically significant differences between local standard herbicide treatments and the glyphosate treatments assessed in this study on the mean values of seed bank, species richness, species diversity and dominance; 2) the data collected on the different parameters showed an enormous variability within sites and years; 3) a dosage of 3 + 3 L ha^-1^ Roundup Ready avoids spread of certain weed species like _Chenopodium album_ or Urtica urens; 3) as far as the standard herbicides were applied correctly in terms of a high and wide efficiency, they will have the same effect as the Roundup Ready treatments.

Effects of Genotype × Environment Interaction on Agronomic Traits in Soybean

Genotype × environment interaction influences the market value of soybean [Glycine max (L.) Merr.] protein, oil, and fatty acid traits. The objectives of this research were (i) to evaluate agronomic trait performance and stability of soybean genotypes in individual environments and across environments; and (ii) to evaluate the relationship of test environments for selecting superior genotypes within the mega‐environment for soybean production in the southern region of Wisconsin. A total of 68 soybean genotypes were selected from University of Wisconsin soybean evaluation trials and grown at four locations in 2003 and 2004. Soybean genotypes, grown in trials with conventional and Roundup Ready herbicide treatments were analyzed for yield, protein, oil, and the fatty acid components palmitic acid, stearic acid, oleic acid, linoleic acid, and linolenic acid. Repeatability estimates among genotypes ranged from 0.27 to 0.98 with yield and the fatty acid component linolenic acid being the most sensitive to environment effects. Superior genotypes could be consistently selected for yield, protein, oil, and fatty acid components using biplot analysis and stability estimates. Among locations in the southern region in Wisconsin, Arlington provides unique information for soybean fatty acid evaluations, but similar information about soybean yield, protein, and oil with Janesville or Lancaster. So, if soybean fatty acid is not important then Arlington could be dropped as a test site.

Influence of Seeding Rate and Herbicide Treatments on Weed Control, Yield, and Quality of Spring‐Seeded Glyphosate‐Resistant Alfalfa

Field trials were conducted in 2005 and 2006 in central and southwest Missouri to investigate the effect of seeding rate and herbicide programs on weed control, forage quality, and yield within the year of establishment in spring seeded glyphosate‐resistant (GR) alfalfa (Medicago sativa L.). In all experiments, EPTC (4.4 kg ha−1), 2,4‐DB plus sethoxydim (1.1 plus 0.21 kg ha−1), imazamox (0.043 kg ha−1) and glyphosate (0.86 kg ae ha−1) were applied to GR alfalfa that was seeded at 4.5, 8.9, 13.5, and 18 kg ha−1 Across all locations, the glyphosate application provided good control of weeds regardless of alfalfa seeding rate. When applied at the same timing, imazamox provided similar levels of annual broadleaf weed control as glyphosate, while 2, 4‐DB plus sethoxydim provided similar levels of annual grass and broadleaf weed control as glyphosate. Neither glyphosate nor the conventional herbicide treatments reduced alfalfa stem density between the first and last annual harvests, but 2, 4‐DB plus sethoxydim resulted in the most visual injury to seedling alfalfa stands and lowered initial yields at all locations. In addition, alfalfa annual yields were similar or higher in the glyphosate treatment compared to the other herbicide programs. Harvested forage in the herbicide treatments generally had greater crude protein (CP) content than the untreated control forage. Application of glyphosate resulted in similar or higher forage CP content compared to conventional herbicide treatments. In vitro true digestibility of the harvested GR alfalfa ranged from 750 to 860 g kg−1 DM at all locations with few differences across herbicide treatments.

Conventional vs. Glyphosate-Resistant Cropping Systems in Ontario: Weed Control, Diversity, and Yield

Glyphosate-resistant (GR) crops have been adopted rapidly since their commercial introduction, and with the increase in commercially available crops resistant to glyphosate, continuous use of the same herbicide mode of action is now possible in some crop rotations. A 6-yr study was initiated to investigate the effects of conventional herbicides compared with continuous use of glyphosate in GR or Roundup Ready corn and GR soybean in a corn–soybean and a corn–soybean–winter wheat rotation. Individual experiments were fully phased and established at three locations under conventional tillage (CT) and at two locations under no-tillage (NT). Results indicated that midseason weed ground cover was lower when weeds were controlled with glyphosate; however, in most cases, this did not result in improved corn or soybean yields. Within locations, species richness, which strongly influenced other diversity indicators, was most affected by the herbicide treatments. Including winter wheat in the crop rotation had little effect on corn and soybean weed ground cover, density, and community structure and only affected soybean yield. Moreover, no effects of herbicide system used in previous corn and soybean were observed in winter wheat, with the exception of species diversity in NT, where species diversity tended to be greater when weeds in previous corn and soybean were treated with conventional herbicides. After 6 yr, the effects of continuous use of GR crops in rotation were similar to those reported in previous studies; however, continued monitoring and longer-term investigations of these systems are necessary to detect the early stages of development of herbicide-resistant biotypes.

Weed Management in Glyphosate- and Glufosinate-Resistant Sugar Beet

Field experiments were conducted to determine the critical period of weed interference in glyphosate- and glufosinate-resistant sugar beet, and to determine if PRE herbicides increased weed control or sugar beet root yield when glufosinate, glyphosate, or conventional POST herbicides were applied. Glyphosate- and glufosinate-resistant sugar beet root yields were reduced by up to 66 and 67%, respectively, when weeds remained all season in the weedy control treatment compared with yields when weed removal occurred as soon as the weeds were 2.5 cm tall, approximately 2 to 3 wk after planting (WAP). A critical period of weed interference did not occur in this research. The critical time of weed removal was approximately 8 WAP in 1998 and beyond 11 WAP in 1999. Weeds averaged 20 cm in height at 8 WAP and weed densities were greater in 1998 compared with 1999. The critical weed-free period for glyphosate- and glufosinate-resistant sugar beet was 4.5 to 5 WAP in 1998. In 1999, the critical weed-free period at the Michigan Sugar location was 1.5 WAP in glyphosate-resistant sugar beet, and 6.5 WAP in glufosinate-resistant sugar beet for the Michigan Sugar site. Glyphosate or glufosinate POST provided better weed control and resulted in greater sugar beet root yield compared with conventional POST herbicides when data were combined over PRE herbicide treatments. PRE herbicides improved the control of common lambsquarters andAmaranthusspecies in some of the site-years when data were combined over POST treatments, but sugar beet yield did not increase. Our research suggests that PRE herbicides will not be necessary in glyphosate- or glufosinate-resistant sugar beet. To avoid sugar beet yield loss, multiple POST applications of glyphosate or glufosinate will be needed until 6 to 9 WAP to prohibit yield loss from weeds emerging after the last POST application.

Evaluation of herbicide programs for the management of glyphosate-resistant waterhemp ( Amaranthus rudis) in Maize

Field experiments were conducted in corn to evaluate the influence of herbicide treatments on glyphosate resistant waterhemp control in Platte County, Missouri during 2006 and 2007. Pre-emergence (PRE), pre-emergence followed by post-emergence (PRE fb POST), and post-emergence-only (POST-only) herbicide programs were evaluated for use in conventional, glyphosate-resistant, or glufosinate-resistant corn hybrids. All programs containing a PRE herbicide, conventional POST herbicide, or glufosinate resulted in greater than 98% control of glyphosate-resistant waterhemp and reduced seed production by at least 99%. Waterhemp densities were also reduced by programs that contained a PRE herbicide, conventional POST herbicide, or glufosinate. The highest waterhemp density and poorest control occurred with a sequential glyphosate program. Corn yields did not differ between herbicide treatments in 2006 however certain conventional PRE and PRE fb POST programs increased yields compared to the sequential glyphosate program in 2007. Results from this research indicate that several herbicide options are available for the control of glyphosate-resistant common waterhemp in corn. However, the lack of crop rotation at this field site for a period of at least 15 consecutive years and lack of residual herbicide applications typically utilized in corn likely contributed to the increased sensitivity of this waterhemp population to PRE-only corn herbicide programs.

Alternative Management of Roadside Vegetation

Management of vegetation is an important element of roadside maintenance for safety and aesthetics. Current methods of management by highway departments principally involve mowing and the use of conventional, chemical herbicides. This research addressed use of herbicides (citric acid, clove oil, corn gluten meal, and pelargonic acid) that are considered as alternatives to conventional herbicides and the use of mechanical treatments of woodchip and bark mulches and burning. These alternative methods were compared with the use of conventional herbicides to assess the relative efficacy of treatments on roadside sites. A single application of pelargonic acid demonstrated immediate or short-term suppression of growth of vegetation; however, the efficacy lasted for no more than 6 weeks, after which regrowth was not distinguishable from untreated vegetation. Repeated applications of pelargonic acid will be necessary for season-long efficacy. Formulations of citric-acetic acid gave no control or only weak suppression of vegetative growth soon after application, and no suppression was evident after 6 weeks, suggesting that these materials have only limited use in roadside environments. The effects of burning lasted for about 6 weeks. No suppression of growth of roadside vegetation occurred with the use of corn gluten meal, which acted as a nitrogen fertilizer to promote growth. Mulches of bark or woodchips were strongly suppressive against emerging vegetation for 2 years, but were more effective in the first year than in the second year after application. The costs of materials and labor for the alternative practices were substantially more than for the conventional herbicides used in this study.

Alternative Management of Roadside Vegetation

Management of vegetation is an important element of roadside maintenance for safety and aesthetics. Current methods of management by highway departments principally involve mowing and the use of conventional, chemical herbicides. This research addressed use of herbicides (citric acid, clove oil, corn gluten meal, and pelargonic acid) that are considered as alternatives to conventional herbicides and the use of mechanical treatments of woodchip and bark mulches and burning. These alternative methods were compared with the use of conventional herbicides to assess the relative efficacy of treatments on roadside sites. A single application of pelargonic acid demonstrated immediate or short-term suppression of growth of vegetation; however, the efficacy lasted for no more than 6 weeks, after which regrowth was not distinguishable from untreated vegetation. Repeated applications of pelargonic acid will be necessary for season-long efficacy. Formulations of citric-acetic acid gave no control or only weak suppression of vegetative growth soon after application, and no suppression was evident after 6 weeks, suggesting that these materials have only limited use in roadside environments. The effects of burning lasted for about 6 weeks. No suppression of growth of roadside vegetation occurred with the use of corn gluten meal, which acted as a nitrogen fertilizer to promote growth. Mulches of bark or woodchips were strongly suppressive against emerging vegetation for 2 years, but were more effective in the first year than in the second year after application. The costs of materials and labor for the alternative practices were substantially more than for the conventional herbicides used in this study.

Molecular Investigations of the Soil, Rhizosphere and Transgenic Glufosinate-Resistant Rape and Maize Plants in Combination with Herbicide (Basta®) Application under Field Conditions

A field study was conducted during 1994 to 1998 on the Experimental Farm Roggenstein, near Fürstenfeldbruck, Bavaria, Germany to determine the effect of transgenic glufosinate-resistant rape in combination with the herbicide Basta [glufosinate-ammonium, phosphinothricin, ammonium (2RS)-2-amino-4-(methylphosphinato) butyric acid] application on soil microorganisms and the behaviour of the synthetic transgenic DNA in response to normal agricultural practice. No influence of Basta on microbial biomass could be detected. The phospholipid fatty acid analysis of soil extracts showed no difference between Basta application and mechanical weed control, whereas conventional herbicide application revealed a different pattern. Basta application resulted in a changed population of weeds with a selective effect for Viola arvensis. During senescence, transgenic rape DNA was degraded similar to endogenous control DNA. After ploughing the chopped plant material in the soil, transgenic as well as endogenous control DNA sequences could be detected for up to 4 weeks for rape and up to 7 months for maize, whereas PCR analysis of composted transgenic maize revealed the presence of the transgene over a period of 22 months.

Ocorrência de insetos na parte aérea da soja em função do manejo de plantas daninhas em cultivar convencional e geneticamente modificada resistente a glyphosate

Com o objetivo de verificar a ocorrência de insetos da parte aérea na cultura da soja convencional e geneticamente modificada resistente a glyphosate, realizou-se este trabalho durante a safra agrícola 2004/05, em Cruz Alta, RS, na área experimental da Fundação Centro de Experimentação e Pesquisa (FUNDACEP). A semeadura foi realizada no dia 26/11/2004, no delineamento experimental de blocos ao acaso com parcelas subdivididas e com quatro repetições, em esquema fatorial 2 x 3. O fator A correspondeu à cultivar "CD 214 RR" resistente a glyphosate e à "CD 201" convencional e o fator B correspondeu ao sistema de manejo das plantas daninhas (sem controle, controle mecânico e controle químico tradicional) e com um tratamento adicional (controle químico com glyphosate na cultivar "CD 214 RR"). A utilização da soja geneticamente modificada resistente a glyphosate e a aplicação do herbicida glyphosate alteraram a ocorrência de algumas espécies de insetos-praga e inimigos naturais na parte aérea da soja.

Mulched cover crops as an alternative to conventional weed management systems in vineyards

SummaryConventional methods of weed management in vineyards rely primarily on herbicides and tillage. The desire to adopt alternatives to these methods is driven by environmental and economic reasons. Weed suppression and grape yield under mulched cover crop systems at two rainfed northern California vineyards were similar to, and at times exceeded, those under conventional tillage or herbicide management. Cover crop productivity was positively correlated with weed suppression and mulch decomposition rates and seemed to be determined primarily by location and then by cover crop type. The mulch from mowed cover crops averaged 603(± 94) gm−2 at the two sites. Weed suppression was linked to light interception by the mulch cover for most weed species. Subterranean clover planted directly in the vine row significantly reduced weed cover where it established. The increased dominance of the perennial Convolvulus arvensis and reduction of certain annual species was indicative of species compositional changes in all treatments. Profits under the cover cropping systems exceeded those under conventional tillage and herbicide systems by € 794 ha−1 averaged over the duration of the experiment at both locations.

Weed Population Dynamics after Six Years under Glyphosate‐ and Conventional Herbicide‐based Weed Control Strategies

Field studies using glyphosate‐resistant corn (Zea mays L.), sugarbeet (Beta vulgaris L.), and spring wheat (Triticum aestivum L.) were conducted at Scottsbluff, NE, Torrington, WY, and Fort Collins, CO, over 6 yr to evaluate weed population dynamics under glyphosate‐ and conventional herbicide–based weed control strategies. We report the response of common lambsquarters (Chenopodium album L.), wild buckwheat (Polygonum convolvulus L.), and all grasses combined to four management strategies imbedded in two crop rotations. There were no consistent or highly significant benefits from a diverse crop rotation versus continuous corn when weed control was considered. Rotating herbicide mode of action for general weed control provided no benefit above that provided by glyphosate at 0.8 kg acid equivalent (ae) ha−1 applied twice each year. There was no evidence that any weed species developed resistance to glyphosate. The most striking finding of these studies was the buildup of common lambsquarters and wild buckwheat that occurs when glyphosate is applied at 0.4 kg ae ha−1 twice each year. Such a low‐use‐rate approach is to be completely discouraged since it appears to enrich the gene pool for individuals that survive low rates of glyphosate. The continuing decline in the real cost of glyphosate should eliminate any legitimate reason for growers to consider using less than the full labeled rate of glyphosate. All treatments that included glyphosate at all three locations over 6 yr provided significantly better grass control than the nonglyphosate conventional treatments.

Industry Views of Minor Crop Weed Control

The level of past industry participation in registering herbicide minor crop uses has been a function of active ingredient discovery output and the combination of incentives and barriers that drive minor use registration decisions. Over the past 10 yr there have been several external factors negatively impacting the rate of new herbicide introductions by industry. These include industry consolidation, a decrease in the global value of the conventional herbicide market, adoption of Herbicide-Resistant Crop (HRC) technology, a substantial increase in required regulatory activity primarily through reregistration programs, and increased costs of discovery research and product development. The increased cost of conducting business in an increasingly competitive market has undoubtedly influenced herbicide registrants to adopt different discovery strategies. Economics dictate registration efforts only towards crops that will create a significant, positive return on investment. In most cases, development of new herbicides for minor crops is not economically viable due to low or negative return on investment and disproportionate liability risk. Therefore, to motivate increased participation, companies need incentives and mechanisms to mitigate risk and registration barriers. Increased data protection and the Interregional Project 4 (IR-4) program, a cooperative government program with the goal of developing data to support regulatory clearances of pest control products for specialty crops, are current government programs in place that provide incentives and defray cost. Other incentives should be explored to make minor crops more attractive targets. However, product registration, liability risk, and dedicating the necessary resources to adequately research crop selectivity are still major economic barriers. Creative solutions that ensure companies are not unreasonably exposed to yield loss claims would remove a primary reason why companies are reluctant to register herbicides for minor crops.

Yield Environment Affects Glyphosate‐Resistant Hybrid Response to Glyphosate

The yield response of glyphosate‐resistant corn (Zea mays L.) to glyphosate across a broad range of temporal yield environments is not well understood. Field experiments were conducted at three Michigan locations over a five year period (2002–2006) comparing corn grain yield of glyphosate‐resistant hybrids as affected by a glyphosate‐based or conventional herbicide system. Regression analyses of yield data showed a dual glyphosate‐resistant hybrid yield response to glyphosate based on the temporal yield environment for a given year. Under average‐ to low‐yield environments, the glyphosate‐based herbicide system resulted in greater grain yield. However, under temporal high yield environments, the conventional herbicide system resulted in greater grain yield. Threshold corn grain yields above which the conventional herbicide system resulted in higher grain yield and below which the glyphosate‐based herbicide system resulted in higher grain yield were determined to be: 11.38 (± 0.13), 12.73 (± 0.14), 13.97 (± 0.25), and 11.62 (± 0.10) Mg ha−1 respectively for the Huron, Montcalm, Saginaw, and combined site average. Differences in weed control levels were not observed and weed control did not appear to be a factor in grain yield determination. The results suggest a slight corn grain yield reduction from glyphosate under certain temporal high‐yield environments.

Compatibility of a Biological Control Agent With Herbicides for Control of Invasive Plant Species

Abstract Kudzu, Pueraria montana var. lobata, is an exotic invasive weed that is difficult to control with available products and management practices. The fungal pathogen, Myrothecium verrucaria, is being developed as a bioherbicide for kudzu and other invasive vines. This biological control agent might be applied with conventional herbicides to improve the efficacy or spectrum of weed control. The survival of M. verrucaria was measured over time in simulated tank-mixes of commercial formulations of the herbicides: amniopyralid (Milestone*), metsulfuron (Escort XP), and fluroxypyr (Vista). The fungus was also grown in vitro in the presence of these herbicides to evaluate any growth inhibition. M. verrucaria was highly tolerant to all concentrations of amniopyralid and metsulfuron for up to two days in simulated tank-mixes, while mixtures with fluroxypyr resulted in a gradual loss of spore viability. The fungus grew on media supplemented with amniopyralid and metsulfuron with only small effects on the gro...

Preparation and applications of controlled release systems based on intercalated atrazine salt and polymeric atrazine salt onto montmorillonite clay

Polymer–clay composites carrying atrazine and polymeric atrazine salts as new controlled release systems have been prepared. Polymeric atrazine was prepared by polycondensation of atrazine with diethyl 2,3- O-dichloroacetyl-tartrate and diethyl-tartrate. The intercalation of the atrazine and polymeric atrazine salts onto MMT was carried out through cation exchange process. The characterizations of the prepared materials were determined by a various analytical techniques. The release rate of the active herbicide from the products was determined in both aqueous medium at different pH and salt concentration and in soil column. The release from the intercalated compound in the soil takes place within one month, while the free atrazine was lost completely through leaching after four days. The pots and field applications of the intercalated compounds on some herbs and maize were investigated. The results of this study showed high activity of the prepared compounds on the herbs inhibition and in the same time increasing the growth rate of maize compared with the conventional herbicide.

Dose- and time - dependent abundance of some soil-microbes at chlorsulfuron herbicide application

Introduction Intensification of crop production practices, has enhanced the pesticide use in the agriculture. Among the xenobiotics the herbicides are the most frequently applied agrochemicals (KECSKES, 1976), for improve the yield-production and quality. Apart from the desired toxic effects of some herbicides on weeds, however, the treatments may also have adverse effects on non-target organisms in the soil, in plants (SZENTPETERY et al. 2005, JOLANKAI et al. 2006) and the rhizosphere, like to other results on the GMO-s (VILLANYI et al. 2006). Either the structure or the function of microbial communities may be influenced by pesticide applications. In case of some herbicides the fast degradation, metabolisation is also known by several soil microbes (KATAI et al. 2002). Mechanisms of such toxic or metabolic effects are highly depending on the types and rates of pesticides, the chemical formulations and also the microbial species, exposed. Herbicides are generally most toxic to phototrophic microorganisms through the disruption of photosynthesis (DELORENZO et al. 2000). Beside the reduced applyed rates, the “new generation” herbicides are offering less harmful effects to the beneficial soil-living organisms, by keeping its weed-control capacity throughout the whole vegetation periods (NAGY, 1989). In the agriculture in comparison with conventional herbicides, the Glean (with a 75 % of chlorsulfuron content) can be still 100 times more efficient against the weeds. Regarding the soil biological consequences, an active role in the detoxification of chlorsulfuron by moulds and Actinomycetes was reported in an earlier study (JOSHI et al., 1985). The biodegradation pathway of chlorsulfuron, operated by Aspergillus niger, a common soil fungus was studied under laboratory conditions by BOSCHIN et al. (2003). The fate of chlorsulfuron herbicid could be potentially managed by some soil-microbes in the soils. Several microbial groups from the soil was studied, therefore in their sensitivity to the various doses of the chlorsulfuron (Glean 75) herbicide. There was a timedependent effect considered, when the 3-weeks and 3-months abundance was also assessed in a soil-incubation model-experiment. A simplified, rapid and economic plating method was developed to estimate the abundance of specific microbes from the herbicide treated soil at different application rates.

Statistical models to evaluate invertebrate–plant trophic interactions in arable systems

Over the past 40 years there have been marked shifts in arable farmland management that are widely believed to have had a considerable impact on flowering plants and invertebrates and the small mammals and birds that rely upon them. It is not yet possible to predict the dynamics of plants and invertebrates either with past or future changes in farmland management. This study investigates whether a basic invertebrate classification, formed of broad trophic groups, can be used to describe interactions between invertebrates and their resource plants and evaluate management impacts for genetically modified, herbicide-tolerant (GMHT) and conventional herbicide management in both spring- and winter-sown oilseed rape. It is argued that the analyses validate trophic-based approaches for describing the dynamics of invertebrates in farmland and that linear models might be used to describe the changes in invertebrate trophic group abundance in farmland when driven by primary producer abundance or biomass and interactions between invertebrates themselves. The analyses indicate that invertebrate dynamics under GMHT management are not unique, but similar to conventional management occurring over different resource ranges, and that dynamics differed considerably between spring- and winter-sown oilseed rape. Thus, herbicide management was of much lower impact on trophic relationships than sowing date. Results indicate that invertebrate dynamics in oilseed rape are regulated by a combination of top-down and bottom-up trophic processes.

Effects of glyphosate and foliar amendments on activity of microorganisms in the soybean rhizosphere

A field study was conducted to determine the effects of glyphosate on microbial activity in the rhizosphere of glyphosate-resistant (GR) soybean and to evaluate interactions with foliar amendments. Glyphosate at 0.84 kg ae ha− 1 was applied GR soybean at the V4–V5 development stages. Check treatments included a conventional herbicide tank mix (2003 study only) and no herbicides (hand-weeded). Ten days after herbicide application, a commercially available biostimulant and a urea solution (21.0% N) were applied to soybean foliage at 33.5 mL ha− 1 and 9.2 kg ha− 1, respectively. Soil and plant samples were taken 0, 5, 10, 15, 20 and 25 days after herbicide application then assayed for enzyme and respiration activities. Soil respiration and enzyme activity increased with glyphosate and foliar amendment applications during the 2002 growing season; however, similar increases were not observed in 2003. Contrasting cumulative rainfall between 2002 and 2003 likely accounted for differences in soil microbial activities. Increases in soil microbial activity in 2002 suggest that adequate soil water and glyphosate application acted together to increase microbial activity. Our study suggests that general soil microbial properties including those involving C and N transformations are not sensitive enough to detect effects of glyphosate on rhizosphere microbial activity. Measurements of soil-plant-microbe relationships including specific microbial groups (i.e., root-associated Fusarium spp.) are likely better indicators of impacts of glyphosate on soil microbial ecology.